Polymerase chain reaction assays for monitoring antiviral therapy and making therapeutic decisions in the treatment of acquired immunodeficiency syndrome

ABSTRACT

The present invention relates to methods of monitoring, via polymerase chain reaction, the clinical progression of human immunodeficiency virus infection and its response to antiretroviral therapy. According to the invention, polymerase chain reaction assays may be used to predict immunological decline and to identify, at an early stage, patients whose infection has become resistant to a particular antiretroviral drug regimen.

This application is a divisional application of U.S. Ser. No.09/782,971, filed Feb. 13, 2001 now U.S. Pat. No. 6,503,705, which is acontinuation application of U.S. Ser. No. 09/399,082 filed Sep. 17,1999, abandoned, which is a continuation application of U.S. Ser. No.08/470,885, filed Jun. 6, 1995, now U.S. Pat. No. 5,968,730, which is adivisional application of U.S. Ser. No. 07/883,327, filed May 14, 1992,abandoned. All of these applications and patents are incorporated hereinby reference in their entirety. This invention was made with Governmentsupport under contracts A127762-04 and A127766-07 awarded by theNational Institutes of Health. The Government has certain rights in thisinvention.

1. INTRODUCTION

The present invention relates to methods of monitoring, via polymerasechain reaction, the clinical progression of human immunodeficiency virusinfection and its response to antiretroviral therapy. According to theinvention, polymerase chain reaction assays may be used to predictimmunological decline and to identify, at an early stage, patients whoseinfection has become resistant to a particular antiretroviral drugregimen.

2. BACKGROUND OF THE INVENTION

Human immunodeficiency virus (HIV) isolated from patients treated withzidovudine (AZT) may demonstrate markedly reduced in vitrosusceptibility to AZT (Larder et al., 1989, Science 243:1731–1734; Rookeet al., 1989, AIDS 3:411–415; Land et al., 1990, J. Infect. Dis.161:326–329; Boucher et al., 1990, Lancet 336:585–590; Japour et al.,1991, Proc. Natl Acad. Sci. 88:3092–96; Tudor-Williams et al., 1992,Lancet 339:15–19). This reduced susceptibility has been related to theduration of therapy with AZT and the severity of HIV disease at the timeAZT therapy is begun (Richman et al., 1990, J. AIDS 3:743–756).Nucleotide sequence analysis of AZT-resistant HIV strains has revealed anumber of mutations in the reverse transcriptase (RT) gene associatedwith decreased AZT susceptibility (Larder et al., 1989, Science246:1155–1158; Larder et al., 1991, AIDS 5:137–144; Kellam et al., 1992,Proc. Natl. Acad. Sci. USA 89:1934–1938; St. Clair et al., 1991, Science253:1557–1559; Richman et al., 1991, J. Infect. Dis. 164:1075–1081).Molecular cloning experiments have confirmed that these mutations in theRT gene confer AZT resistance (Larder et al., 1989, Science246:1155–1158; Larder et al., 1991, AIDS 5:137–144; Kellam et al., 1992,Proc. Natl. Acad. Sci. USA 89:1934–1938; St. Clair et al., 1991, Science253:1557–1559). Of these mutations the one at codon 215 resulting in asingle amino acid substitution (Thr→Tyr or Phe) has been shown to be themost common mutation and to have the greatest impact on in vitrosusceptibility to AZT (Larder et al., 1991, AIDS 5:137–144; Richman etal., 1991, J. Infect. Dis. 164:1075–1081; Boucher et al., 1992, J. Inf.Dis. 165:105–110).

Several studies have addressed the relationship between in vitro AZTresistance, mutations in the RT gene and clinical disease. Richman andcoworkers studied 32 patients with different stages of HIV disease anddemonstrated that the development of in vitro AZT resistance was relatedto the duration of therapy with AZT and to the severity of disease atthe time AZT was begun (Richman et al., 1990, J.AIDS 3:743–746). Boucherand coworkers studied HIV P24-antigenemic patients treated with AZT for2 years. They observed that at 6 months, seven patients with a mutationat codon 215 had a weak, non-statistically significant trend towardlower CD4 counts compared to nine patients who were wild type at codon215 (Boucher et al., 1990, Lancet 336:585–590). After 2 years nearly allpatents had the mutation. Tudor-Williams and coworkers studied HIVisolates from 19 symptomatic children treated with AZT for 9–39 monthsand showed that in vitro AZT resistance was associated with poorclinical outcome (Tudor-Williams et al., 1992, Lancet 339:15–19).However, adult studies have not shown a precise correlation between thedevelopment of in vitro resistance and progression of HIV disease.

3. SUMMARY OF THE INVENTION

The present invention relates to methods of monitoring, via polymerasechain reaction (PCR), the clinical progression of human immunodeficiencyvirus (HIV) infection and its response to antiviral therapy. It isbased, in part, on the discovery that plasma HIV RNA copy number, asmeasured using PCR, may be used as a sensitive marker of the circulatingHIV viral load to assess the therapeutic effect of antiretroviralcompounds. In working examples described herein, an increase in plasmaHIV RNA copy number was found to correlate with disease progression, andsuccessful antiretroviral therapy was found to correlate with a declinein plasma HIV RNA copy number.

The invention is also based, in part, on the discovery that geneticchanges in HIV which confer resistance to antiretroviral therapy may berapidly determined directly from patient peripheral blood mononuclearcells (PBMC) and/or plasma HIV RNA using a “nested” PCR procedure. Inworking examples disclosed herein, a mutation at codon 215 of HIVreverse transcriptase (RT) was found to occur in AZT-treated patientswhich correlated with refractoriness to AZT treatment. The mutation wasfound in plasma HIV RNA one to eight months before it was detectable inPBMC. The development of the condon 215 mutation in HIV RT was found tobe a harbinger of immunological decline, which occurred between six andtwelve months after the mutation was detectable in plasma HIV RNA.

In particular embodiments of the invention, PCR assay may be used tomonitor the clinical progression of HIV infection in patients receivingantiretroviral therapy. An increase in plasma HIV copy number detectedby such an assay would correlate with refractoriness to treatment. If apatient being treated with an antiretroviral therapeutic agent exhibitsan increase in plasma HIV RNA copy number, a physician should consideraltering the patients treatment regimen. It should be noted that thepresent invention offers the advantage of being more sensitive inmeasuring HIV virus than standard methods which measure plasma p24antigen or infectious virus detectable by culture techniques.

In further embodiments of the invention, PCR assay may be used to detectmutations at codon 215 of HIV RT which correlate with resistance toantiretroviral therapy and which precede immunologic decline by 6–12months. Once mutation at codon 215 has been detected in a patientundergoing antiretroviral therapy, an alteration in the therapeuticregimen must be considered. The speed at which a modified regimen shouldbe instituted may depend on whether the mutation is present in plasmaHIV RNA or PBMC. If the mutation is present in PBMC, a rapid alterationin therapy may be warranted.

In patients suffering from HIV infection, opportunistic infectionsarising as a result of a compromised immune system can be rapidly fatal.It is therefore extremely important to strive to avoid deterioration ofthe immune system in these patients. Because the present inventionenables the early prediction of immunological decline, it allowsalteration of a patient's therapeutic regimen so as to avoidopportunistic infections, and therefore may be used to promote survivaland improve the quality of life of HIV-infected patients.

4. DESCRIPTION OF THE FIGURES

FIG. 1. Human immunodeficiency virus RNA copy number in 200 μl of plasmafrom 72 subjects as determined by cDNA gene amplification. Of 39patients who were not currently receiving antiretroviral therapy, 20 hada CD4 count <200/mm³ (HIV copy number 1,369±707) and 19 had a CD4 count>200/mm³ (HIV copy number 44±10). Of 33 subjects who were currently onAZT, 14 had a CD4 count <200/mm³ (HIV copy number 295±5) and 19 had aCD4 count >200/mm³ (HIV copy number 16±5). Mean copy number (opencircles) of subjects not on therapy was 690±360 as compared to 134±219for patients currently on AZT (P<0.05, independent sample t test).

FIG. 2. Human immunodeficiency virus RNA copy number in plasma from 27subjects before (pre) and 1 mo after (post) dideoxynucleoside therapy.(∘) AZT; (●) AZT+ddI; and (▴) ddI alone. Mean copy number decreased from540±175 to 77±35 after therapy (P<0.05 paired t test).

FIG. 3. Human immunodeficiency virus RNA copy number in plasma from 9subjects with two samples obtained before initiation of therapy (pre 1and pre 2) and two samples obtained 1 and 2 mo after commencing therapy(post 1 and post 2). (▴) ddI alone; (●) ddI+AZT.

FIG. 4. Serial CD4 counts in PBMC (cells/μl) of 17 patients in which HIVreverse transcriptase carried a mutation at codon 215 (top) and of 21patients in which HIV reverse transcriptase was wild type at codon 215(bottom).

FIG. 5. CD4 cell counts in PBMC from serial time points in 37 patients.∘=wild type sequence in serum specimen, ●=mutant sequence in serum,↑=wild type sequence in PBMC, ↓=mutant sequence in PBMC; A: 16 patientsmutant at codon 215 in both serum HIV RNA and PBMC (proviral DNA). B: 10patients mutant at codon 215 in serum HIV RNA but wild type in theirPBMC. C: 11 patients whom remained wild type at codon 215 in their serumHIV RNA and PBMC.

FIG. 6. Relationship of PBMC to serum genotypes in the 38 patients atstudy endpoint.

FIG. 7. Nucleotide sequences of SK38, SK39, and SK19 (SEQ ID NOS: 6–8).

5. DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to methods of monitoring, via PCR, theclinical progression of HIV infection in patients receivingantiretroviral therapy. For purposes of clarity and not by way oflimitation, the detailed description of the invention is divided intothe following subsections:

-   -   (i) PCR assay of plasma HIV RNA;    -   (ii) PCR assay of peripheral blood mononuclear cells;    -   (iii) PCR assay for mutation at codon 215 of HIV reverse        transcriptase; and    -   (iv) utility of the invention.

It should be noted that heparin appears to have an inhibitory effect ongene amplification via PCR. It is therefore desireable to avoid usingheparin as an anticoagulant of patient blood samples. If herapin hasbeen used in a sample, the sample nay be purified of heparin, forexample, by collecting virus by ultracentrifugation.

5.1 PCR Assay of Plasma HIV RNA

According to the invention, it is desireable to avoid degradation of RNAin plasma samples prior to measurement of HIV RNA copy number.Therefore, in preferred embodiments of the invention, guanidinium isadded to plasma or serum samples prior to storage at a concentration ofabout 2.5M and samples are kept frozen at −70° C., with no samplesstored for longer than about 3 months. Serum may be used interchangeablywith plasma according to the invention.

RNA may be extracted from plasma using standard techniques, such asthose set forth in Chomczynski and Sacchi, 1987, Ann. Biochem.162:156–159. For example, 200 μl of clarified plasma to which 200 μl of5M guanidinium thiocyanate had previously been added may be extractedwith phenol/chloroform and precipitated with isopropanol. The resultingpellet may then be washed in 75 percent ethanol, dried, and brought upinto solution in diethylpyrocarbonate-treated glass distilled water.

From plasma RNA, WV RNA may be transcribed to cDNA using a suitablereverse transcriptase (for example, Moloney murine leukemia virusreverse transcriptase) using standard techniques, such as for example,those set forth in Kawasaki, 1990, in “PCR Protocols: A Guide to Methodsand Applications,” Innis et al., eds., Academic Press, Berkeley, Calif.pp. 21–27. Any suitable primer for amplification of HIV genomic RNAsequences may be used, including, but not limited to, the oligomersSK38, SK39, and SK19 (FIG. 7) described in Kellog et al., 1990, in “PCRProtocols: A Guide To Methods and Applications,” Innis et al., etds.,Academic Press, Berkeley, Calif. pp. 337–347. In a preferred embodimentof the invention, HIV cDNA may be amplified as follows: to a 100μreaction mixture, cDNA prepared as described supra may be added,together with 50 pmol of primers SK38 and SK39, 10 mM of each dNTP, 10mM Tris (pH 8.3), 2.5 mM MgCI₂, 50mM KC1, and 2.5 U of RECOMBITAQ DNApolymerase (Perkin-Elmer Cetus, Norwalk, Conn.). The mixture may then beoverlaid with 50 μl of mineral oil, and tubes containing the reactionmay be placed in a DNA thermal cycler (e.g. Perkin-Elmer Cetus) forabout 30 cycles of amplification with the following program: 95° C.30seconds, 55° C./30 seconds, and 72° C./60 seconds for denaturation,annealing, and extension, respectively. Negative and positive controlswhich include both high and low copy number HIV RNA and DNA may be addedat each step.

It is important that the number of cycles not exceed 35, and preferably,only about 30 cycles of amplification are used in the PCR. Using agreater number of cycles may detract from the sensivity of the assay.

The copy number of HIV RNA may then be measured by methods known to theskilled artisan. For example, the number of copies of HIV RNA in apatient sample may be quantiated by hybridizing the product of the abovePCR with a detectably labeled probe that is complementary to HIVsequence. The amount of signal generated by probe hybridized to PCRproduct may then be compared to the amount of signal generated by probehybridized to a known copy number of HIV. Probe may be detectablylabeled by an enzyme, a radioisotope, a fluorescent compound, achromogenic compound, or any other detectably labeled compound.

In a preferred, nonlimiting embodiment of the invention, at least one ofthe PCR primers may be biotinylated, probe may be labeled withhorseradish peroxidase (HRP), and copy number may be evaluated by anenzyme-linked affinity assay as follows. 96-well microplates (Maxisorp;Nune, Naperville, Ill.) may be coated with 100 μl of a 0.1mg/mi solutionof avidin (Sigma Chemical Co., St. Louis, Mo.) in 50 mM Na₂CO₃ (pH 9.6)overnight at room temperature. Wells may then be washed twice with PBS,and then filled with 300 μl of a blocking solution containing5×Denhardt's solution, 1% gelatin (Sigma), 250 μl/ml sheared herringsperm DNA (Promega Biotec, Madison, Wis.) at least overnight at 40° C.Immediately before use, the blocking solution may be aspirated from eachwell and 5 μl of PCR product prepared as described supra (using at leastone biotinylated primer) may be added to each well together with 65 μlof a hybridization solution containing 5×saline sodium phosphate EDTA,5×Denhardt's solution; and 1 pmol of HRP-labeled SK19 HIV gag-specificprobe. Because HIV primer was biotinylated, HIV amplified sequencesshould selectively adhere to the avidin-coated wells, so that a captureand hybridization reaction may be carried out for 1 hour at 42° C. Eachwell may then be washed about 20 times with PBS containing 0.05%TWEEN20™(polyoxyethylene sorbitan monolaureate), for example, using aBiomek™ 1000 Automated Workstation (Beckman Instruments, Inc., PaloAlto, Calif.). The HRP substrate O-phenylenediamine (Sigma) may then beprepared at 0.6 mg/ml in 0.1 M citrate buffer (pH 5.5) containing 0.03%hydrogen peroxide, and 150 p.1 of this solution may be added to eachwell. After about 10 minutes the reaction may be stopped with 1N H₂SO₄and the optical density of each well measured at 490 run, for example bythe Biomek 1000. A lower level of positivity had been defined as anabsorbance of 0.135. This cutoff value was calculated from the meanabsorbance obtained from a group of seronegative samples plus threestandard deviations. Copy number from subject samples may be determinedfrom the absorbances obtained from a dilution series of an RNA gag geneconstruct of known copy number (Holodniy et al., 1991, J. Infect. Dis.163:862–866).

In an alternate preferred, specific embodiment, RNA collected fromplasma may be reverse-transcribed by using 500 ng of primer A(5′-TTCCCATTAGTCCTATT-3′) (SEQ ID NO:1) and 5 units of MuLV RT (BethesdaResearch Labs) in 10 μl of amplification buffer (25 mM kCL, 50mM TrisHCl pH 8.3, 0.1 mg/ml bovine serum albumin, 1.45 mM each of dATP, dGTP,dCTP and dTTP, 1.5 mM MgCl₂, and 2.5 U of RNasin (Promega)) for 10 mm.at room temperature, then 30 minutes at 42° C. followed by heatinactivation at 95° C. for 5 mm. This cDNA may then be amplified by PCRusing 250 ng of primer NE1 (5′-TCATTGACAGTCCAGCT-3′) (SEQ ID NO:2) in areaction mixture (100 μl) containing the same buffer as above with 0.25mM of each dNTP and 2.5 U of AMPLITAQ DNA polymerase, using about 30cycles of 94° C. for 1 mm., 45° C. for 1 mm, and 72° C. for 2 mm, togenerate a 768 bp region of the HIV pol gene.

5.2 PCR Assay of Peripheral Blood Mononuclear Cells

Peripheral blood mononuclear cells (PBMCs) may be used fresh orfollowing cryopreservation (e.g. at −190° C.). DNA may be prepared fromPBMCs using standard techniques for use in detection of HIV proviralDNA. Any suitable HIV primer oligonucleotide(s) may be used in PCR todetect HIV provirus.

In a preferred, nonlimiting embodiment of the invention, cryopreserved(−190° C.) PBMC may be treated with a lysis buffer (for example, 0.45percent TWEEN-20™ (polyoxyethylene sorbitan monolaureate), 10 mM TrisHCl pH 8.0, 2.5 mM MgCl₂, 50 mM KCl, and 0.1 mg/ml proteinase K) forabout two hours at 56° C. and then heat inactivated at 95° C. for 10minutes. Approximately 1 μg of DNA (20 μl of the PBMC lysate) may beused in the initial PCR amplification with primers A(5′-TTCCCATTAGTCCTATT-3′) (SEQ ID NO:1) and NE1(5′-TCATTGACAGTCCAGCT-3′) (SEQ ID NO:2) with reaction conditions as setforth in Larder et al., 1991, AIDS 5:137–144 to generate a 768 bp regionof the HIV pol gene.

5.3 PCR Assay for Mutation at Codon 215 of HIV Reverse Transcriptase

To analyse the changes in codon 215 of the HIV pol gene, a “double” or“nested” PCR procedure was performed using the primers, reagents, andreaction conditions described by Larder et al., 1991, AIDS 5:137–144.Five μl of the 768 bp product generated by PCR with primers A(5′-TTCCCATTAGTCCTATT-3′) (SEQ ID NO:1) and NE1(5′-TCATTGACAGTCCAGCT-3′) (SEQ ID NO:2) and either plasma HIV RNA orPBMC DNA may be used in a second series of nested PCR amplificationsusing primers that detect wild-type sequence or sequence mutated atcodon 215. In preferred, non-limiting embodiments of the invention, thefollowing primers may be used: to detect wild-type sequence primers B(5′-GGATGGAAAGGATCACC-3′) (SEQ ID NO:3) and 3 W(3′-TGGTGTGGTCTGTTTTTTGTA-5′) (SEQ ID NO:4) and to detect mutants atcodon 215, primers B (supra) and 3M (3′-AAGTGTGGTCTGTTTTTTGTA-5′) (SEQID NO:5). PCR may then be performed as follows. About 1 μl of templatemay be used per PCR reaction in 100 μl containing 25 mM KCl, 50 mM TrisHCl pH 8.3, 0.1 mg/ml bovine serum albumin (BSA), 0.2 mM each of dATP,dGTP, dCTP and dTTP, 0.25 μl of each oligonucleotide primer, and 1.5 mMMgCl₂. Reaction mixtures may be heated at 100° C. for two minutes priorto addition of TAQ DNA polymerase (2.5 U, Perkin-Elmer Cetus, Conn.),overlaid with 100 μl of light mineral oil, and subjected to 30 cyclesconsisting of a denaturation step (1 minute, 94° C.), primer annealing(30 seconds, 45° C.) and DNA synthesis (30 seconds, 72° C.) using, forexample, a Perkin Elmer Cetus DNA thermal cycler. Ten p1 of PCR productfrom each set of “nested” PCR reactions may then be analyzed todetermine the presence and intensity of the products. For example, PCRreactions may be analyzed on a 3.0 percent agarose gel with ethidiumbromide staining; a portion of a patient sample subjected to “nested”PCR using primers B and 3W may be run in a lane next to another portionof the same patient sample subjected to “nested” PCR using primers B and3M. A 210 bp PCR product would be expected; if the patient samplecontained HIV RT having the codon 215 mutation, the lane carrying primerB/3M PCR product should exhibit a band that is more intense than anycorresponding band in the primer B/3W lane. If the patient samplecontained only wild type HIV RT, the band in the primer B/3W lane shouldbe more intense than any corresponding band in the primer B/3M lane.Alternatively, if the patient sample contained a mixture of wild typeand mutant HIV RT, bands of similar intensities should be in both lanes.

5.4 Utility of the Invention

The present invention relates to methods of monitoring, via PCR, theclinical progression of HIV infection in patients receivingantiretroviral therapy. Techniques described in Sections 5.1 through 5.3supra, may be used as set forth below.

In one particular embodiment, the present invention provides for amethod of evaluating the effectiveness of antiretroviral therapy of apatient comprising (i) collecting a plasma sample from an HIV-infectedpatient who is being treated with an antiretroviral agent; (ii)amplifying the HIV-encoding nucleic acid in the plasma sample using HIVprimers in about 30 cycles of PCR; and (iii) testing for the presence ofHIV sequence in the product of the PCR; in which the absence ofdetectable HIV sequence correlates positively with the conclusion thatthe antiretroviral agent is therapeutically effective and the presenceof detectable HIV sequence correlates positively with the conclusionthat the antiretroviral agent is therapeutically ineffective. Infurther, related, embodiments, the presence of detectable HIV sequencecorrelates positively with an absolute CD4 count of less than 200cells/mm³, and the absence of detectable HIV sequence correlatespositively with a CD4 count greater than 200 cells/mm³. The phrase“correlates positively,” as used herein, indicates that a particularresult renders a particular conclusion more likely than otherconclusions.

In another particular embodiment, the present invention provides for amethod of evaluating the effectiveness of antiretroviral therapy of apatient comprising (i) collecting a plasma sample from an HIV-infectedpatient who is being treated with an antiretroviral agent; (ii)amplifying the HIV-encoding nucleic acid in the plasma sample using HIVprimers in about 30 cycles of PCR; and (iii) measuring the HIV RNA copynumber using the product of the PCR, in which an HIV RNA copy numbergreater than about 500 correlates positively with the conclusion thatthe antiretroviral agent is therapeutically ineffective, and an HIV RNAcopy number less than about 200 correlates positively with theconclusion that the antiretroviral agent is therapeutically effective.

In a further embodiment, the present invention provides for a method ofevaluating the effectiveness of antiretroviral therapy of a patientcomprising (i) collecting one pre-treatment plasma sample from anHIV-infected patient who is about to be treated with an antiretroviralagent; (ii) collecting a post-treatment plasma sample from theHIV-infected patient after the patient has been treated with theantiretroviral agent; (iii) amplifying the HIV-encoding nucleic acid inthe pre-treatment and post-treatment plasma samples using HIV primers inabout 30 cycles of PCR; (iv) measuring the HIV RNA copy number using theproducts of the PCRs of step (iii); and (v) comparing the HIV RNA copynumber in pre-treatment and post-treatment plasma samples, in which aratio of HIV RNA copy number in pre-treatment and post-treatment plasmasamples of greater than about 4 to 1 correlates positively with theconclusion that the antiretroviral agent is therapeutically effective.

In additional embodiments of the invention, PCR assay may be used todetect mutations at codon 215 of HIV RT which correlate with resistanceto antiretroviral therapy and which precede immunologic decline by 6–12months. Accordingly, the present invention provides for a method ofevaluating the effectiveness of antiretroviral therapy of a patientcomprising (i) collecting a plasma sample from an HIV-infected patientwho is being treated with an antiretroviral agent; and (ii) determining(for example, using “nested” PCR) whether the plasma sample comprisesnucleic acid encoding HIV RT having a mutation at codon 215, in whichthe presence of the mutation correlates positively with immunologicdecline of the patient within a six to twelve month period. Under suchcircumstances, the HIV virus infecting the patient has become, via themutation, resistant to the antiretroviral agent. It therefore maybedesirable after detecting the mutation, to either increase the dosage ofantiretroviral agent, change to another antiretroviral agent, or add oneor more additional antiretroviral agents to the patient's therapeuticregimen. For example, if the patient was being treated with zidovudine(AZT) when the mutation arose, the patient's therapeutic regimen maydesirably be altered, within about a six to twelve month period of themutation's occurrence, by either (i) changing to a differentantiretroviral agent, such as dideoxyinosine (ddI) and stopping AZTtreatment; or (ii) increasing the dosage of AZT; or (iii) adding anotherantiretroviral agent, such as ddI, to the patient's therapeutic regimen.The effectiveness of the modification in therapy may be evaluated, asset forth above, by monitoring the HIV RNA copy number. A decrease inHIV RNA copy number correlates positively with the effectiveness of atreatment regimen.

Because the mutation at the 215 codon appears first in plasma HIV RNAand later in PBMC proviral DNA, once the mutation is detected inproviral DNA, the treatment regimen is desirably modified with haste inorder to avoid immune decline. Accordingly, the present inventionprovides for a method of evaluating the effectiveness of antiretroviraltherapy of a patient comprising (i) collecting PBMC from an HIV-infectedpatient who is being treated with an antiretroviral agent; and (ii)determining whether the PBMC comprise proviral HIV DNA which comprises amutation at codon 215, in which the presence of the mutation correlatespositively with immunologic decline of the patient within a 4–11 monthperiod (because, as discussed in Section 7, infra, a mutation in serumHIV RNA was found to precede the mutation in proviral DNA by 1–8months). Once the mutation is detected in proviral DNA, immune declinebecomes even more imminent, and alteration of the patient's therapeuticregimen is desirable.

When immune decline is heralded by the increase in HIV RNA copy numberand/or the presence of the mutation at codon 215, in addition toaltering the patient's antiretroviral therapy, it may also be desirableto treat the patient prophylactically for opportunistic infections,using antifungal, antibiotic, and/or antiparasitic medications.

Antiretroviral agent, as used herein, includes any known antiretroviralagent including, but not limited to, dideoxynucleosides. In preferredembodiments of the invention the antiretroviral agent is AZT. Resistanceto certain antiretroviral agents, including AZT, is associated with amutation at codon 215. Resistance to other antiretroviral agents, suchas ddI, is associated with a mutation at codon 74 The present inventionprovides for analogous techniques in which the effectiveness ofantiretroviral therapy is monitored by determining whether plasma HIVRNA or PBMC contain a mutation at codon 74 of HIV RT, in which amutation at that locus may augur immunological decline and may warrant amodification of antiretroviral therapy.

One preferred, non-limiting, specific embodiment of the invention is asfollows: A method of evaluating the effectiveness of AZT therapy of apatient comprising (i) collecting a plasma sample from an HIV-infectedpatient who is being treated with AZT; (ii) amplifying the HIV-encodingRNA in the plasma sample by converting the RNA to cDNA and amplifyingHIV sequences using HIV primers in about 3.0 cycles of PCR; and (iii)testing for the presence of HIV sequence in the product of the PCR, inwhich the absence of detectable HIV sequence correlates positively withthe conclusion that AZT is therapeutically effective and the presence ofdetectable HIV sequence correlates positively with the conclusion thatAZT is therapeutically ineffective. In most preferred embodiments, theHIV primers used comprise NE1 (supra), SK38 and/or SK39 (supra), and/orthe presence of HIV sequence is detected using an enzyme-linked assay(e.g., a horseradish peroxidase based assay). Similar embodiments inwhich the HIV copy number is measured are also provided for.

Another preferred, non-limiting, specific embodiment of the invention isas follows: A method of evaluating the effectiveness of AZT therapy of apatient comprising (i) collecting a plasma sample from an HIV-infectedpatient who is being treated with AZT; (ii) amplifying the HIV-encodingRNA in the plasma sample by converting the RNA to cDNA and amplifyingHIV sequences using HIV primers that result in a PCR product thatcomprises that portion of the RT gene that contains the 215 codon (e.g.primer NE1, supra); (iii) performing “nested” PCR using primers thatresult in PCR products that reflect the presence of wild type (e.g.primers B and 3W, supra) or 215 codon mutant (e.g. primers B and 3M,supra); and (iv) determining, via the products of “nested” PCR, thepresence or absence of a mutation at codon 215 of the HIV RT, in whichthe presence of the mutation correlates positively with immunologicdecline of the patient within a six to twelve month period. An analogousmethod may be used in which the patient sample is PBMC, and the presenceof a mutation is proviral DNA is determined.

6. EXAMPLE Reduction in Plasma Human Immunodeficiency Virus RibonucleicAcid After Dideoxynucleoside Therapy as Determined by the PolymeraseChain Reaction 6.1 Materials and Methods

6.1.1 Patients

After informed consent was obtained, whole blood samples were collectedby venipuncture in the presence of acid-citrate-dextrose as ananticoagulant. A single plasma sample was collected from 39 HIVantibody-positive subjects who were not receiving antiretroviral therapyat the time of collection and from 33 HIV antibody-positive subjects whowere currently on and had received AZT for a minimum of 3 mo.

Two plasma samples were collected from an additional 27 subjects beforeand 1 month. after initiation of dideoxynucleoside therapy. 18 of thesesubjects received 500 mg/d of AZT orally. Seven subjects received acombination of zidovudine (150–600 mg/d) and 2′,3′-dideoxyinosine(ddI)(134–500 mg/d). Two patients received 500 mg/d of ddI alone (seeTable I for individual subject characteristics). Finally, nine of thesesubjects had two plasma samples taken 1–3 wk. before initiatingantiretroviral therapy and two plasma samples taken 1 and 2 mo. aftercommencing therapy. Plasma was separated within 4 h. by centrifugationat 500 g for 10 min. A second centrifugation was performed on the plasmaat 500 g for 30 min. to remove any cellular material. 200 μl of plasmawas then mixed with 200 μl of a solution containing 5 M guanidiniumthiocyanate, vortexed briefly, and stored at −70° C. until further use.All samples were assayed within 3 mo. of collection. To decreasevariance, all specimens to be compared from the same subject were run inthe same assay.

6.1.2 Extraction of RNA from Plasma

RNA was extracted from plasma by the method described in Chomczynski etal., 1987, Ann. Biochem. 162:156–159. Briefly, 200 μl of clarifiedplasma to which 200 μl of 5 M guanidinium thiocyanate had previouslybeen added was extracted with phenol/chloroform and precipitated withisopropanol. The resulting pellet was then washed in 75% ethanol, dried,and brought up in diethylpyrocarbonate treated, glass distilled water.

6.1.3 Reverse Transcription and Amplification of cDNA

HIV RNA was transcribed to cDNA using Moloney murine leukemia virusreverse transcriptase (Bethesda Research Laboratories, Gaithersburg,Md.) by the method described in Kawasaki, 1990, “In PCR Protocols: AGuide to Methods and Applications” pp. 21–27, M. A. Innis, D. H.Gelfand, J. J. Sninsky, and T. J. White, eds. Academic Press, Berkeley,Calif. Oligomers used for amplification included SK38, SK39, and SK19(Kellog et al., 1990, “In PCR Protocols: A Guide to Methods andApplications,” pp. 337–348, M. A. Innis, D. H. Gelfand, J. J. Sninsky,and T. J. White, eds. Academic Press, Berkeley, Calif.). Biotinylationof SK38 and horseradish peroxidase (HRP) labeling of probe SK19 wereprepared as described in Levenson et al., 1990, “In PCR Protocols: AGuide to Methods and Applications,” pp. 99–112 M. S. Innis, D. H.Gelfand, J. J. Sninsky, and T. J. White, eds. Academic Press, Berkeley,Calif. Amplification of HIV cDNA was carried out as follows: to a 100-μAreaction mixture was added the cDNA, 50 pmol of primers SK38 and SDK39,10 mM of each dNTP, 10 mM Tris (pH 8.3), 2.5 mM MgCl₂, 50 mM KCl, and2.5 U of RECOMBITAQ DNA polymerase (Perkin-Elmer Cetus, Norwalk, Conn.).The mixture was then overlaid with 50 μl of mineral oil. Tubes wereplaced in a DNA thermal cycler (Perkin-Elmer Cetus) for 30 cycles ofamplification with the following program: 95° C./30 s, 55° C./30 s, and72° C./60 s for denaturation, annealing, and extension, respectively.Negative and positive controls which included both high and low copynumber WV RNA and DNA were added at each step.

6.1.4 Enzyme-Linked Affinity Assay

To detect and quantitate PCR product, 96-well microplates (Maxisorp;Nunc, Naperville, Ill.) were coated with 100 μl of a 0.1 mg/ml solutionof avidin (Sigma Chemical Co., St. Louis, Mo.) in 50 mM Na₂CO₃ (pH 9.6)overnight at room temperature. Wells were then washed twice with PBS.Wells were then filled with 300 μl of a blocking solution containing5×Denhardfs solution, 1% gelatin (Sigma), 250 μl/ml sheared herringsperm DNA (Promega Biotec, Madison, Wis.) at least overnight at 4° C.Immediately before use, the blocking solution was aspirated from eachwell and 5 μl PCR product and 65 μl of a hybridization solution,containing 5×saline sodium phosphate EDTA, 5×Denhardt's solution, and 1pmol of HRP-labeled SK19 HIV gag specific probe was added to each well.A capture and hybridization reaction was then carried out in the wellfor 1 h. at 42° C. The 96-well microplate was then placed in a Biomek™100 Automated Workstation (Beckman Instruments, Inc., Palo Alto, Calif.)where wells were washed 20 times with BPS containing 0.05% TWEEN-20™(polyoxyethylene sorbitan monolaureate). The HRP substrateO-phenylenediamine (Sigma) was prepared at 0.6 mg/ml in 0.1 M citratebuffer (pH 5.5) containing 0.03% hydrogen peroxide. 150 μl of thissubstrate solution was added to each well. After 10 mm. the reaction wasstopped with 1 NH₂SO₄ and the optical density of each well measured at490 nm by the Biomek 1000. A lower level of positivity had been definedas an absorbance of 0.135. This cutoff value was calculated from themean absorbance obtained from a group of seronegative samples plus threestandard deviations. Copy number from subject samples were determinedfrom the absorbances obtained from a dilution series of an RNA gag geneconstruct of known copy number described in Holodniy et al., 1991, J.Infect. Dis. 163:862–866. The lower level of sensitivity in this assaywas 40 copies of HIV gag gene RNA.

6.1.5 Plasma HIV Culture and P24 Antigen Assay

Quantitative HIV plasma microculture was performed according to themethod described in Ho et al., 1989, N. Engl. J. Med. 321:1621–1625. P24antigen was detected by an antigen capture assay by a method provided bythe supplier (Abbott Laboratories, North Chicago, Ill.).

6.1.6 Statistical Analysis

Sample optical density was converted to copy number and analysesperformed on samples expressed as RNA copy number/200 μl of plasma. A ttest of independent samples was used in analysis of subject who did notreceive antiretroviral therapy compared to subjects who were receivingAZT. A t test of paired samples was used to analyze paired plasma dataand CD4 counts from subjects pre- and post-therapy. All t tests were twotailed. A Fisher's exact test or chi square test were used for analysisof proportion where appropriate. Statistical significance was defined asP<0.05.

6.2 Results

72 subjects were evaluated in a cross-sectional study of HIV disease todetermine plasma HIV RNA copy number by PCR. The results are presentedin FIG. 1. 39 subjects who were not currently receiving antiretroviraltherapy and 33 subjects who were receiving AZT were evaluated. Untreatedsubjects were more likely to have a positive signal than treatedsubjects (32 of 39 vs. 16 of 33, respectively, P 0.008, chi square). Inthe 39 subjects who were not currently receiving therapy, the meanplasma HIV RNA copy number was 690±360 (mean±SEM) per 200 μl of plasma,while the 33 subjects who had been receiving AZT therapy had a mean copynumber of 134±219 (P<0.05). Mean CD4 count for each group was 316±45 and300±37, respectively (P=NS).

Subgroups were then analyzed with respect to CD4 count. Among those with<200 CD4 cells, untreated subjects were more likely to have positivesignal than treated subjects (18 of 19 vs. 9 of 14, P<0.04, Fisher'sexact test). Among those with >200 CD4 cells, 14 of 20 untreatedsubjects vs. 7 of 19 treated subjects had a detectable signal (P=NS,Fisher's exact test). Untreated subjects with CD4 count <200/mm³ had amean RNA copy number of 1,369±707 and mean CD4 count of 73±17; untreatedsubjects with CD4>200/mm³ had a mean RNA copy number of 44±10 and meanCD4 count of 547±45; treated subjects with CD4 counts <200/mm³ had amean RNA copy number of 295±5 and mean CD4 count of 115±13; and treatedsubjects with CD4 counts >200/mm³ had calculated mean RNA copy number of16±5 (which is below the level of detection of this assay and would beinterpreted as negative) and mean CD4 count of 437±41.

27 additional subjects were then evaluated before and 1 mo afterinitiation of dideoxynucleoside therapy. Clinical parameters of thesubjects are presented in Table I. PCR results are presented in FIG. 2.Results show that plasma HIV RNA copy number fell from 540±175 to 77±35after therapy (P<0.05, paired t test). Mean CD4 count increased from399±24 to 442±25 after 4 wk of therapy (P<0.006, paired t test).

TABLE 1 Clinical Parameters and PCR Analysis of Plasma HIV RNA from 27Patients Patient Antiviral No. treatment Pre/post CD4 Pre/post HIV RNA 1* AZT‡ 647/561 106/90  2* AZT 541/651 130/0   3 AZT 840/874 550/0   4AZT 432/462 100/77   5* AZT 379/415 87/57  6* AZT 428/408 40/42  7 AZT422/345 94/94  8 AZT 420/402 0/0  9 AZT 432/532 93/65 10 AZT 430/430105/52  11 AZT 429/404 123/50  12 ddI + AZT§ 280/220 526/0  13 AZT323/320 78/45 14 AZT 320/456 95/95 15 AZT 353/387 301/0  16 ddI + AZT§309/399 300/0  17 ddI + AZT§ 337/398 260/0  18 ddI∥ 328/310 966/0  19ddI+ AZT¶ 383/491 245/0  20 AZT 404/413 0/0 21 AZT 270/450 958/72  22ddI + AZT¶ 292/344 60/0  23 AZT 320/295 2769/437  24 ddi∥ 222/3703944/0   25 AZT 568/732 2014/925  26 DDI + AZT** 367/473 217/0  27 DDI +AZT** 310/399 439/0  *Remote history of AZT use. “AZT dose 500 mg/dunless otherwise stated. §AZT 300 mg/d + ddI 334 mg/d. ∥ddi 500 mg/d.¶AZT 600 mg/d + ddI 500 mg/d. **AZT 150 mg/d + ddI 134 mg/d.

Finally, 9 of the 27 subjects had two samples taken before initiation oftherapy and two samples taken 1 and 2 months after commencing therapy.The results are presented in FIG. 3. When two pretherapy time pointswere analyzed for constancy of signal, results show that mean copynumber for each pretherapy time point was 945±377 and 643±392.

Two subjects had a second pretherapy sample which was negative. Whenboth pretherapy copy number values were compared to posttherapy values,plasma HIV RNA copy number fell from 794±274 to <40 (which is below thelower level of detection in this assay) after 1 and 2 mo of therapy(P<0.05, paired t test). Mean CD4 count increased from 314±165 to 378±25(P<0.05, paired t test).

Plasma culture was performed on fresh material obtained from the initialpretreatment sample for 23 of 27 of these patients. Only 7 of 23 wereplasma virus positive by culture (from 1 to 100 tissue culture infectivedoes/ml). All 23 of these patients were positive by PCR (>40 copies/200μl). In addition, a p24 antigen test was performed on all 27pretreatment samples. Only 2 of 27 had detectable p24 antigen present(>30 pg/ml).

6.3 Discussion

The results presented here demonstrate that plasma HIV RNA can bedetected and quantified by copy number in the majority of patientsinfected with HIV. In addition, plasma HIV RNA copy number may be usedas a marker of circulating HIV viral load to assess treatment effect ofantiretroviral compounds including dideoxynucleoside compounds. Weinitially conducted a survey to determine whether treatment or degree ofimmunologic impairment, based on CD4 count, affected plasma HIV RNA copynumber. Untreated patients as a group had higher copy numbers thantreated patients. Untreated patients with <200 CD4 cells/mm³ had ahigher mean copy number than patients with >200 CD4 cells/mm³. Likewise,treated patients with <200 CD4 cells/mm³/had higher copy numbers thanpatients with >200 CD4 cells/mm³, indicating that patients with moreadvanced HIV disease have higher circulating copy numbers thanasymptomatic patients, and that the antiretroviral benefit seen inpatients with higher CD4 counts may be waning.

To assess the short-term impact of antiretroviral therapy on patients,27 patients were evaluated before and 1 mo after initiation of AZT, ddI,or combination therapy. As CD4 counts increased after 1 mo of therapy,HIV RNA copy number fell significantly. However, the response ofindividual subjects was variable. 16 of 27 subjects had a markeddecrease in copy number and 11 of 27 did not. Because the majority ofsubjects received AZT alone, it was not possible to assess anydifferences between AZT, ddI, or combination regimens.

Finally, nine subjects had two baseline time points taken in the 3 wkbefore treatment, followed by two monthly samples posttreatment.Pretreatment signal was constant in 7 of 9 subjects, and 2 subjects haddiscordant samples, i.e., one was positive and one was negative. Thiscould be related to real changes in circulating HIV RNA, or introducedduring sample collection, handling, or the assay. However, pretherapyand posttherapy samples were run in the same assay and so were subjectto all of the same reaction conditions. When sample positivity wasconsidered in relation to therapy, 16 of 18 pretherapy samples had apositive signal vs. 0 of 18 posttherapy samples (P<0.001, chi square)showing suppression of HIV RNA copy number with treatment.

Currently there is no standard method to assess circulating viral loadin all HIV-infected patients. Plasma viremia, measured by quantitativemicroculture, can identify and quantify infectious virus in 50–100% ofpatients, principally those with advanced stages of HIV disease, low CD4counts, and p24 antigenemia (Ho et al., 1989, N. Engl. J. Med.321:1621–1625; Coombs et al., 1989, J. Virol. Methods 26:23–21; Ehrnstet al., 1988, N. Engl. J. Med. 324:961–964). Many patients with >200 CD4cells/mm³ do not have detectable infectious plasma viremia. This may bedue to an absence of circulating infectious virus, virus which isneutralized by specific antibody, or the insensitivity of culturetechniques. The results presented here indicate that the majority ofpatients with >200 CD4 cells/mm³ do not have plasma p24 antigen orinfectious virus detectable by culture techniques. In the studiesdescribed herein, it appears that virus undetectable by culture methodswas detectable by PCR methods.

Attempts have been made to assess HIV viral load in patients bymolecular techniques, mainly by quantitative PCR of HIV proviral DNA incirculating mononuclear cells or cell-free virion-associated RNA inplasma. Published data suggest that the number of cells infected withHIV increases with advancing disease and that HIV proviral DNA contentincreases as well. We and others have shown a decrease in HIV proviralDNA with dideoxynucleoside therapy over time (Aoki et al., 1990, AIDSRes. Hum. Retroviruses 6:1331–1339). This was not the case in anotherpublished small series (McElrath et al., 1991, J. Clin. Invest.87:27–30).

We have shown that HIV RNA could be quantified in serum and that copynumber increased with disease progression (Holodniy et al., 1991, J.Infect. Dis. 163:862–866). Plasma HIV RNA has been shown to be presentbefore and after seroconversion with quantitative decreases occurringafter seroconversion (Hewlett et al., 1988, J. Clin. Immunoassay11:161–164). The recent report by Daar et al. (Daar et al., 1991, N.Engl. J. Med. 324:961–964), showed a decrease in both plasma viremia andproviral DNA from PBMC, coinciding with seroconversion after acuteinfection. In one report, plasma HIV RNA levels fell with passiveimmunoglobulin therapy, suggesting a therapy-based response incirculating HIV RNA load (Karpas et al., 1990, Proc. Natl. Acad. Sci.USA 87:7613–7617). Ottman and colleagues have been successful indetecting HIV RNA in plasma from 95% of patients evaluated (Ottman etal., 1991, J. Virol. Methods 31:273–284). They also studied a group ofpatients who were receiving AZT to determine whether there was anytherapeutic impact on HIV RNA signal. 24 of 25 patients who werereceiving AZT had detectable signal. However, methodological differencesin that study vs. the present study may have contributed to thedifferences noted between them. First, Ottman et al. used anultracentrifugation step to sediment virus, enhancing virion-associatedRNA recovery. Second, 40 cycles of amplification after reversetranscription were performed, which would certainly increase thesensitivity of such an assay to successfully detect HIV RNA in virtuallyall patients. Although sensitivity is increased with increased cyclenumber, thus detecting signal in virtually all patients, the ability toshow the quantitative changes demonstrated here with 30 cycles ofamplification is lost.

We have previously shown in serum that quantitative serum cultures werenegative in the majority of patients with >200 CD4 cells/mm³ (Holodniyet al. 1991, J. Infect. Dis. 163:862–866). In the current study, 23plasma samples were evaluated by culture and PCR. All had detectableplasma HIV RNA by PCR<but only seven were plasma HIV-culture positive.Other published experience comparing plasma HIV culture and PCR of HIVRNA from plasma is lacking. Ottman et al. tested only two patients, bothof whom were positive in both assays. Coyle et al. reported that 14 of20 patients had positive plasma cultures and 12 of 20 patients haddetectable HIV RNA in plasma, but no information was given regardingconcordance or discordance of samples (Coyle et al., 1990, Clin. Res.38:778a (Abstr.)).

The type of plasma sample and method of processing and storage werefound to be very important. The type of anticoagulant used for samplecollection can affect detection of plasma RNA. We have previously shownthat plasma collected in the present of herapin does not allow detectionof signal because of an inhibitory effect of heparin on geneamplification (Holodniy et al., 1991, J. Clin. Microbiol. 29:676–679).Although Coyle et al. (1990, Clin. Res. 38:778a (Abstr.)) founddetectable signal from plasma collected in the presence of herapin, anultracentrifugation step preceding RNA analysis lead to removal of mostof the heparin from the enzyme-mediated assay system. However, nocomparison experiments among anticoagulants were performed todemonstrate any attenuation of signal obtained in the presence ofheparin.

Because of our concern for RNA degradation during specimen storage andfreeze thawing, we decided to store fresh plasma at −70° C. in thepresence of guanidinium and process samples within 3 mo of collection.Samples were stored in guanidinium for RNAase inhibition. Preliminarydata from our laboratory would suggest that plasma HIV RNA signal decayswith time in the absence of this RNA stabilizer.

In summary, we have shown that plasma HIV RNA copy number can bequantitated by PCR and does decrease with dideoxynucleoside therapy. Thenonisotopic, microplatebased format presented here makes it possible toprocess multiple patient samples with replicates in a singleamplification and assay run.

7. EXAMPLE Relationship of a Mutation in the HIV Reverse TranscriptaseGene to Decline in CD4 Lymphocyte Numbers in Long Term AZT Recipients7.1 Materials and Methods

7.1.1 Study Population

Cryopreserved PBMC and serum from 40 participants in AIDS Clinical TrialGroup (ACTG) protocols 019 (30 patients) and 016 (10 patients) atStanford University Medical Center AIDS Clinical Trial Unit were used inthis study. Patients at enrollment in these studies were AZT naive,had >200 CD4 cells/μl and had few (016) or no symptoms (019) referableto HIV infection. They were subsequently treated with AZT for 2 to 4years. The most common dosage was 500 mg per day. Approximately onethird of patients received either 1200 mg or 1500 mg per day during theinitial part of their therapy, but were changed to 500 mg per day whenlower doses were found to be as effective but less toxic than higherdoses (Fischl et al., 1990, N. Engl. J. Med. 323:1009–1014; Volberdinget al., 1990, N. Engl. J. Med. 322:941–949). All samples were obtainedfrom the patients while they were on the protocols and thus no patientdeveloped an AIDS defining diagnosis.

7.1.2 CD4 Cell Counts

CD4 cell counts were obtained approximately every three months on eachpatient. All counts were performed at Stanford's ACTG-qualifiedcytofluorometry lab. Samples were stained with monoclonal antibodies toCD3, CD4, and CD8. The absolute CD4 count was calculated by multiplyingthe percent CD4 by the total lymphocyte count.

7.1.3 PBMC Preparation

Cryopreserved (−190° C.) PBMC were treated with a lysis buffer (0.45%TWEEN-20™ (polyoxyethylene sorbitan monolaureate), 10 mM Tris HCl pH8.0, 2.5 mM MgCl₂, 50 mM KCl, and 0.1 mg/ml proteinase K) for 2 hours at56° C. and then heat inactivated at 95° C. for 10 mm. Approximately 1 μgof DNA (20 μl of the PBMC lysate) was used in the initial PCRamplification with primers A(5′-TTCCCATTAGTCCTATT-3′) (SEQ IDNO:1) andNE1(5′-TCATTGACAGTCCAGCT-3′) (SEQ ID NO:2) with reaction conditions asdescribed in Larder et al., 1991, AIDS 5:137–144 to generate a 768 bpregion of the HIV pol gene.

7.1.4 Serum HIV RNA Preparation

Cryopreserved (−70° C.) serum was thawed and then 350 μii of sera wasadded to 350 μl of solution D (Chomczynski et al., 1987, Anal. Biochem.162:156–159) (guanadinium thiocyanate +2-mercaptoethanol) and vortexed.RNA was then extracted with phenol and chloroform and precipitated withethanol as described in Chomczynski et al., 1987, Anal. Biochem.162:156–15918. HIV RNA was then reverse transcribed to cDNA by using 500ng of primer A and 5 units of murine leukemia virus (MuLV) reversetranscriptase (Bethesda Research Labs) in 10μl of amplification buffer(25 mmol/L KCl, 50 mmol/L Tris HCl Ph 8.3, 0.1 mg/ml bovine serumalbumin, 1.45 mmol/L each of dATP, dGTP, dCTP and dTTP, 1.5 mmol/LMgCl₂, 2.5 units of RNasin (Promega)) for 10 mm at room temperature,then 30 mm at 42° C. followed by heat inactivation at 95° C. for 5 mm.This cDNA was then amplified by PCR using 250 ng of primer NE1 in areaction mixture (100 μl) containing the same buffer as above with 0.25mmol/L of each dNTP and 2.5 units of AMPLITAQ DNA polymerase(Perkin-Elmer Cetus). This reaction mixture underwent 30 cycles of 94°C. for 1 mm, 45° C. for 1 mm and 72° C. for 2 min to generate a 768bpregion of the HIV pol gene.

7.1.5 PCR Analysis of HIV Reverse Transcriptase Gene

To analyze the changes in codon 215 of the HIV pol gene, a “double” PCRprocedure was performed using the primers, reagents, and reactionconditions described in Larder et al., 1991, AIDS 5:137–144. Five μl ofthe 768 bp product generated by PCR with primers A and NE1 was used in asecond series of nested PCR amplifications using primer B and 3W todetermine if a wild type sequence was present, or B and 3M to determineif a mutant sequence was present (primer sequences as set forth supraand in Larder et al., 1991, AIDS 5:137–144). Samples were run withnegative, positive and reaction mixture controls. Ten μl of PCR productfrom each of the second set of PCR reactions were analyzed on a 3.0%agarose gel with ethidium bromide staining. PCR products were consideredto have a mutant or wild type sequence by the method described byBoucher et al. (1990, Lancet 336:585–590; 1992, J. Infect. Dis.165:105–110) and Larder et al., 1991, AIDS 5:137–144: a sample wasconsidered to contain the wild type sequence at codon 215 ifamplification with the primers B and 3W resulted in a 210 bp PCR productof highest intensity; a sample was considered to contain a mutantsequence at codon 215 if amplification with the primers B and 3Mresulted in a 210 bp PCR product of highest intensity. The sample wasconsidered to have a mixture of wild type and mutant sequences ifamplification occurred with both primers 3M and 3W resulting in PCRproducts of similar intensity. If a mixture was detected by PCR thenthat sample was included in the mutant group in our statisticalanalysis.

7.1.6 AZT Sensitivity Assay

Patient PBMC were cocultured with mitogen-stimulated PBMC from healthyHIV-seronegative donors. Supernatants from these cultures were collectedand frozen when the HIV P24 antigen concentration exceeded 10,000 pg/ml.30–100 TCID₅₀ (50% tissue culture infectious dose) of virus stock wasused to infect one million donor PBMC pretreated with differentconcentrations of AZT (0.0 uM, 0.005 uM, 0.05 uM, 0.5 uM, 5.0 uM). After7 days, P24 antigen was measured in the cell free supernatant from thecultures with and without zidovudine. The concentration of AZT requiredto inhibit P24 production by 90% (IC₉₀) as compared to the drug freecultures was determined by nonlinear regression analysis (Chou et al.,1984, Adv. Enzyme Regulation 22:27–55). In this assay, the IC₉₀s fromAZT-naive patients ranged from 0.002 μM to 0.038 μM AZT.

7.1.7 Statistical Analysis

All comparisons between the patients with mutant and wild type strainswere performed using the student's t-test. The calculations on the IC₉₀sdetermined by the zidovudine sensitivity assay were performed using thelog₁₀ transformed IC₉₀ (i.e. geometric means were used rather thanarithmetic means).

7.2 Results

7.2.1 PCR Analysis of Codon 215 in PBMC

Proviral DNA was detected by nested PCR in the PBMC of 38 of 40 patientsafter a mean 34 month treatment period. The two patients in whomproviral DNA could not be detected had high CD4 counts at the time theirPBMC were analyzed (729 and 676 cells/μl). PCR amplification of the PBMCfrom 17 of 38 patients (45%) yielded a 210 bp product with the mutantprimer, indicating the presence of a mutation at codon 215 (Thr to Tyror Phe). The PBMC from 21 of 38 patients (55%) demonstratedamplification product only with the wild type primer (a 210 bp product)indicating the presence of Thr at codon 215.

The mean length of therapy and starting CD4 counts for the two groupswere similar (Table 2). However, the 17 patients with a mutation atcodon 215 of HIV RT in PBMC proviral DNA had a 50% decrease in theirabsolute CD4 count between the time they began therapy (378 cells/μl)and the end of the study (189 cells/μl). The 21 patients with a wildtype sequence at codon 215 experienced a mean 11% increase in theirabsolute CD4 count between the time they began therapy (397 cells/μl)and the end of the study (424 cells/μl). The post-treatment CD4percentages of the two groups of patients were also significantlydifferent (25% in patients with wild-type sequence vs 14% in patientswith a mutation in RT at codon 215) (Table 2). The CD4 counts at eachtime point for each patient are shown in FIG. 4.

TABLE 2 CORRELATION OF PATIENT CD4 COUNT CHANGES WITH PCR ANALYSIS OFCODON 215 OF HIV REVERSE TRANSCRIPTASE IN PBMC Wildtype Mutant Number ofpatients 21 17 p Months of AZT 33 ± 8  35 ± 7  0.4 Starting CD4measurements Absolute CD4 (cells/μl) 397 ± 124 378 ± 96  >0.5 CD4% 26 ±8  25 ±  6 >0.5 CD4 measurements at a time of PCR analysis Absolute CD4(cells/μl) 424 ± 210 189 ± 98  <0.0001 CD4% 25 ± 9  14 ± 6  0.00017.2.2 PCR Analysis of Codon 215 in HIV RNA from Serum

20 Serial PBMC samples from earlier time points were available on 8/40patients; however, serial serum samples from earlier time points wereavailable on 37/40 patients. In these 37 patients, 135 serum sampleswere tested for the presence of a codon 215 mutation. In 87% of thesesamples (117), reverse transcribed cDNA could be detected by PCR.Fifteen of the 18 sera that were negative by PCR had been previouslysubjected to multiple freeze-thaws and therefore could be falselynegative. As all patients were AZT-naive, they were assumed to be wildtype at codon 215 at the start of AZT therapy.

Twenty-six of the 37 patients developed a mutation in their HIV RNA.This included the 16 who were also mutant in their PBMC at the end ofthe study period (FIG. 5A), and ten patients who were wild type in theirPBMC but mutant in serum HIV RNA at the end of the study period (FIG.5B). The time preceding the occurrence of the 215 mutation in theirserum ranged from 2 to 44 months of therapy. Among these 26 patients,the mean CD4 count at the start of therapy was 398±139 cells/μl andtheir mean CD4 count at the time of first detection of a codon 215mutation in their serum was 444±206 cells/μl. Nineteen of the 26patients with a codon 215 mutation in their serum had follow-up CD4counts at least 12 months after the mutation was first detected. Inthese 19 patients, there was a mean decrease of 100±116 CD4 cells/μul(25% decline) at six months and a mean decrease of 170±121 CD4 cells/μl(40% decline) at 12 months.

The 11 patients who remained wild type in their serum over the entire 34month period of zidovudine therapy had an increase of 7±92 CD4 cells/μl(2% increase), (FIG. 5C). The mean CD4 count at the start of therapy forthe patients who later developed a mutant in their serum was 398±139cells/μl and this was not significantly different than the starting CD4counts for those patients who remained wild type (397±115 cells/μl,p>0.5). The average length of therapy for both groups was 34 months.

7.2.3 Serum Virus Compared to PBMC Provirus

At the final evaluation of the 38 patients after a mean 34 months ofzidovudine, 11 patients were wild type in both serum and PBMC, 17 weremutant in both serum and PBMC, and 10 patients had a mutation in theirserum but remained wild type in their PBMC FIG. 6. Eight of the 17patients with a mutation in proviral DNA at the end of the study periodhad at least one PBMC sample available from an earlier time point. Inthese eight patients, a mutation in serum HIV RNA preceded the mutationin proviral DNA by 1–8 months. The findings in these 8 patients and inthe 10 patients who were wild type in their PBMC but mutant in theirserum shows that detection of the serum mutation precedes detection ofthe mutation in PBMC. In no instance, did a mutation in patient's PBMCprecede its appearance in serum.

7.2.4 AZT Sensitivity Results Determined by Cell Culture

In vitro AZT susceptibility testing was performed on 17 of 38 patientsusing a different aliquot of the same post-treatment PBMC that were usedfor the PCR analysis. The geometric mean of the IC₉₀s of eight patientswith the wild type form at 215 was 0.04 μm AZT (range: 0.02–0.28 μm);the geometric mean IC₉₀ of nine patients with a mutation at codon 215was 0.41 μm AZT (range: 0.03–8.0 μM; p=0.002).

7.3 Discussion

As an increasing number of HIV infected individuals are offered earlytreatment with AZT, the significance of drug resistant virus has becomean important question. In the present study we found a strongcorrelation between the presence of a mutation at codon 215, which islinked to AZT resistance and an accelerated decline in CD4 cell number.The patients we studied all began taking AZT when their CD4 cell numberswere relatively high and before the onset of AIDS. We observed that the17 patients with a mutation at codon 215 in proviral DNA in their PBMCexperienced a mean 50% decrease in their CD4 count between the time thatthey began therapy and the time that their cells were analyzed formutations. The 21 patients who were wild type at codon 215 in theirproviral DNA at the end of treatment experienced a mean 11% increase intheir CD4 count during the same time period.

Patient cells were only available during the last year of the study.However, by extracting and reverse transcribing HIV RNA from patient'sserum specimens we were able to detect codon 215 mutation at earliertime points. The patients in our study with and without a mutation inserum HIV had similar starting CD4 counts (397+115 vs. 398±139, p>0.5)and similar lengths of therapy (34 months in both groups). Yet we foundthat those patients who develop a mutation in HIV RNA had a subsequent40% decline in their CD4 cells over the next 12 months. The patients whoremained wild type in their serum had a 2% increase in their CD4 cellsover 34 months of therapy.

These results show that genetic changes in the virus which confer drugresistance can be rapidly determined directly form patient PBMC and HIVRNA in patients serum using a nested PCR procedure. By using PCR we wereable to detect viral nucleic acid in 90% of PBMC samples and 87% ofserum samples. Techniques which require culturing HIV from PBMC or serummay select HIV subpopulations with greater tropism for certain cells(Kusumi et al., 1992, J. Virol. 66:875–885; Meyerhans et al., 1989, Cell58:901–910). This may complicate the analysis of the clinicalsignificance of AZT resistance detected by phenotypic assays.

Earlier clinical studies focused on AZT resistance in patients withinitially low CD4 cell counts or who were at high likelihood of diseaseprogression. Furthermore, these studies tested HIV isolates which hadbeen passaged in culture. In contrast, in this study we did not selectpatients at high likelihood for disease progression but instead weincluded all patients who remained on AZT for at least 2 years and whohad high CD4 counts at the beginning of the study; codon 215 mutationsin serum virus occurred early in treatment. The mean CD4 count at thefirst appearance of the mutation was higher than the CD4 count at thestart of therapy (444 vs. 398 cells/μl). This suggests that mutation ofthe reverse transcriptase gene is not dependent upon low CD4+ T cells.On the other hand, we also found that a large percentage of patientsremained wild type at codon 215 and phenotypically sensitive to AZTdespite almost 3 years of therapy. This may be because our patients wereless advanced in their disease or that by using PCR instead of coculturewe were able to include patients whose virus might not have grown inculture. These results also suggest that the PBMC may not be the initialsource of mutant virus, as evidenced in 18 of our patients where theserum HIV RNA mutation preceded that in PBMC by many months. The sourceof the mutant HIV detected in serum may be cells in lymphatic, centralnervous system or reticuloendothial sites.

The significance of specific mutations in the RT gene with respect toAZT resistance has been defined in patient isolates as well as throughmolecular cloning experiments (Larder et al., 1989, Science246:1155–1158; Larder et al., 1991, AIDS 5:137–144; Kellam et al., 1992,89:1934–1938; St. Clair et al., 1991, Science 253:1557–1559). Of thefour mutations first reported to be associated with AZT resistance(codons 67, 70, 215, 219), the mutation at codon 215 has been shown tobe the most commonly occurring and to have the greatest impact onsusceptibility. This impact on AZT susceptibility will vary depending onwhether or not additional mutations are present (Larder et al., 1989,Science 246:1155–1158; Larder et al., 1991, AIDS 5:137–144; Kellam etal., 1992, 89:1934–1938; St. Clair et al., 1991, Science 253:1557–1559;Richman et al., 1991, J. Infect. Dis. 164:1075–1081; Boucher et al.,1992, J. Infect. Dis. 165:105–110). Recent sequencing studies ofclinical isolates suggest that there are additional mutations in the RTgene that may contribute to AZT resistance (Japour et al., 1991, Proc.Natl. Acad. Sci. 88:3092–96; Kellam et al., 1992, Proc. Natl. Acad. Sci.USA 89:1934–1938; St. Clair et al., 1991, Science 253:1557–1559).However, the occurrence of the two consecutive nucleotide changesnecessary for the amino acid change at codon 215 may be the mostimportant requirement for the development of resistance (Kellam et al.,1992, Proc. Natl. Acad. Sci. U.S.A. 89:1934–1938; Richman et al., 1991,J. Infect. Dis. 164:1075–1081; Boucher et al., 1992, J. Infect. Dis.165:105–110). In this study, a subset of 17 patients were tested using acell culture assay which confirmed that the viruses with a mutation atcodon 215 had reduced susceptibility to AZT.

The patients with resistant or sensitive virus in our study had similarCD4 counts at the start of AZT therapy and received AZT for a similarperiod of time. Therefore, the development of resistance and a mutationat codon 215 could not be attributed to any known pretreatmentcharacteristic. None of our patients developed AIDS during our studyperiod and the patients who developed a mutation in their serum HIV RTdid so at a relatively high CD4 count. Thus, advanced stage of HIVdisease could not explain why some patients developed a mutation whileothers did not. Additional characteristics of the patient or virus mayexplain why one HIV strain develops a mutation and another does not. Ithas been stated that syncytium-inducing, T-cell tropic isolates inHIV-infected individuals contribute to the CD4 cell decline (Tersmetteet al., 1989, Lancet 1:983–985). If an HIV isolate can maintain a highlevel of replicative events despite the presence of AZT, this viruswould have a much greater likelihood of mutation. Treatment with AZT mayselect both syncytium-inducing and drug resistant virus. Selection ofmore virulent HIV population under prolonged AZT pressure may explainwhy some patients experienced a CD4 cell decline in the months after theRT mutation arose.

The present report shows a strong association between the presence of aHIV RT mutation and declining CD4 counts in AZT treated patients.Furthermore, it demonstrates that a HIV mutation known to cause AZTresistance can be detected prior to a decline in CD4 cell number.

1. A method of evaluating the effectiveness of anti-HIV therapy of apatient comprising: correlating the presence or absence of detectableHIV-encoding nucleic acid in a plasma sample of an HIV infected patientwith an absolute CD4 count, wherein the presence or absence of saiddetectable HIV-encoding nucleic acid is determined by (i) collecting aplasma samples from an HIV-infected patient who is being treated with anantiretroviral agent; (ii) amplifying HIV-encoding nucleic acid that maybe present in the plasma sample using HIV primers via PCR and; (iii)testing for the presence of HIV-encoding nucleic acid sequence in theproduct of the PCR.
 2. The method of claim 1, wherein the absence ofHIV-encoding nucleic acid and the absolute CD4 count being greater thanabout 200 cells per cubic millimeter correlate positively with theconclusion that the antiretroviral agent is therapeutically effective.3. The method of claim 1, wherein the presence of HIV-encoding nucleicacid and the absolute CD4 count being less than about 200 cells percubic millimeter correlate positively with the conclusion that theantiretroviral agent is therapeutically ineffective.
 4. The method ofany one of claims 1–3, wherein the PCR is performed for about 30 cycles.5. The method of any one of claims 1–3 in which the HIV primers are SK38and SK39.
 6. The method of any one of claims 1–3 in which one HIV primeris primer NE1 (5′TCATTGACAGTCCAGCT-3′) (SEQ ID NO:2).
 7. The method ofany one of claims 1–3 in which one HIV primer is primer A(5′-TTCCCATTAGTCCTATT-3′) (SEQ ID NO:1).
 8. The method of any one ofclaims 1–3 in which the antiretroviral agent is zidovudine.